The present invention relates to a servo transfer press system that includes a servo press that performs press working, and a servo transfer device that transfers a workpiece, and is configured so that a press operation can be performed according to a reference press motion based on a press phase signal that is synchronized with a master phase signal, and a transfer operation can be performed according to a reference transfer motion based on a transfer phase signal that is synchronized with the master phase signal.
A servo transfer press system includes a servo press that performs press working, and a servo transfer device that transfers a workpiece.
The servo press includes a plurality of press-working stations, and performs press working (e.g., punching, bending, or drawing) on the workpiece using a die while moving a slide upward and downward. The slide is moved upward and downward according to a press motion. Note that the workpiece transferred to the first press-working station is a material. A semi-finished product is obtained by each intermediate press-working station, and a product is obtained by the final press-working station. The motion of the slide according to the press motion is referred to as “slide motion”.
A press is roughly classified into a non-servo press and a servo press depending on the presence or absence of motion variability. The non-servo press rotates the crank shaft at a constant speed using a synchronous motor or the like, and performs a press operation according to a constant sine-wave press motion. In contrast, the servo press can perform a press operation while setting an arbitrary slide motion by changing the rotation of the crank shaft using a servomotor.
For example, the servo press can perform a press operation according to an operation press motion indicated by the solid line in FIG. 16 in which the slide is set at a position lower than the top dead center position (e.g., a half-stroke symmetrical motion with respect to bottom dead center). In FIG. 16, the horizontal axis indicates time, and the vertical axis indicates the slide position. The working cycle time can be reduced as compared with the non-servo press by reducing the stroke, so that the production efficiency can be significantly improved. Note that the motion indicated by the dotted line in FIG. 16 is a reference press motion when the crank shaft of the servo press is rotated at a constant speed. In this case, the slide position moves along an approximate sine curve with respect to time in the same manner as in the non-servo press.
As illustrated in FIG. 17, the servo press can also perform a press operation according to a press motion in which the slide is temporarily stopped at the desired position during downward movement, and is moved downward again when a given time has elapsed. For example, a magnesium alloy is held by the die heated at a high temperature until the magnesium alloy is heated to the optimum temperature, and is press-worked when the magnesium alloy has reached the optimum temperature, and the die is quickly moved upward after completion of press working. The magnesium alloy can be pressed with high efficiency by utilizing the above press motion instead of the reference press motion.
The transfer device transfers the workpiece to each press-working station. More specifically, the transfer device is configured so that the workpiece is held by a workpiece-holding tool (e.g., finger or cup) provided on a feed bar, and transferred while moving the feed bar in two-dimensional or three-dimensional directions. The feed bar may be referred to as “transfer bar”. The transfer device may be driven by a synchronization drive method that causes the transfer device to perform a transfer operation using a drive shaft that can be synchronized with the motion of the press, or a servo transfer drive method that causes the transfer device to perform a transfer operation while setting an arbitrary transfer motion by changing the rotation of the feed shaft using a servomotor. It is advantageous to use the servo transfer drive method from the viewpoint of operation adaptability.
It is necessary to drive the servo press and the servo transfer device in synchronization. A method that causes the servo transfer device to transfer the workpiece in synchronization with the rotation of the crank shaft of the servo press based on the crank shaft angle of the servo press has been employed (see JP-B-7-73750 and JP-B-7-75741). Specifically, the start timing and the end timing of each transfer motion are generated and output based on the rotation angle of the crank shaft (crank shaft angle follow-up method).
However, it is difficult to deal with various press motions (including the press motions illustrated in FIGS. 16 and 17) required for the servo press when using the crank shaft angle follow-up method. Since the crank shaft angle follow-up method causes the servo transfer device to follow the servo press, the press operation directly affects the transfer motion. Specifically, a smooth transfer motion may easily be impaired. Moreover, it takes time to match the press motion and the transfer motion.
In order to solve the above problems, JP-A-2005-297010 proposes a master phase signal synchronization method that causes the servo press to perform a press operation according to a reference press motion based on a press phase signal that is synchronized with the phase velocity of a master phase signal (e.g., process number), and causes the servo transfer device to perform a transfer operation according to a reference transfer motion based on a transfer phase signal that is synchronized with the phase velocity of the master phase signal.
The master phase signal synchronization method makes it possible to ensure that the servo transfer device performs a smooth and reliable transfer motion, and the servo press exhibits satisfactory characteristics (i.e., flexible slide motion characteristics).
The master phase signal synchronization method ensures a stable and smooth transfer press operation after adjusting each phase signal with respect to the master phase signal. However, a further improvement has been desired along with the wide-spread use of the master phase signal synchronization method.
For example, it may be desired to change only the press motion in order to improve the productivity and the product quality. However, when the transfer press operation is performed in a state in which only the press motion is changed, the relative phase relationship between the slide motion and the transfer motion based on the master phase signal changes. In this case, interference may occur between the slide motion and the transfer motion.
In order to prevent interference between the slide motion and the transfer motion, it is necessary to adjust each phase signal with respect to the master phase signal, and change the synchronization setting when implementing the slide motion of the servo press and the transfer motion of the servo transfer device. It is also necessary to check whether or not interference between the slide motion and the transfer motion (i.e., interference between the servo press and the servo transfer device) occurs while operating the servo press and the servo transfer device at a low speed.
Specifically, these operations must be performed before actual operation each time the press motion is changed. Therefore, an improvement in operability and adaptability to multikind and small quantity production has been strongly desired.
The above problems also occur when it is desired to change only the transfer motion, or it is desired to change both the press motion and the transfer motion. Therefore, it has been strongly desired to solve the problems.